1. Field of the Invention
The invention relates to a light source unit, and more particularly to a light source unit which is capable of preventing temperature increase therein.
2. Description of the Related Art
As a liquid crystal display device has been fabricated in a larger size, a liquid crystal display device is required to have a higher brightness and a wider view angle.
In order to accomplish a higher brightness in a liquid crystal display device, transmissivity of a liquid crystal panel and an efficiency at which a light is used have been improved. However, there is a limitation in such ways, and hence, a brightness in a light source unit is presently tried to increase.
A wider view angle in a liquid crystal display device is often accompanied with a demerit that a transmissivity of a liquid crystal panel is deteriorated. In order to compensate for such a demerit, a brightness in a light source unit is required to increase.
That is, a higher brightness in a light source unit would accomplish a higher brightness and a wider view angle in a liquid crystal display device.
However, it would be necessary to supply an increased power to a light source unit in order to accomplish a higher brightness in a light source unit. It is well known that about 10 to 40% of an energy emitted from a light source unit is lost as heat radiation. That is, as an increasing power is supplied to a light source, heat generated in the light source increases, and heat loss also increases.
If a light source increasingly generates heat, a liquid crystal panel positioned in the vicinity of the light source would be heated accordingly, resulting in that display quality in the liquid crystal panel would be degraded because the liquid crystal panel has a display characteristic which is influenced by heat.
Thus, there has been a demand for a liquid crystal display device which is capable of accomplishing a higher brightness without degradation in display quality.
As a solution to the above-mentioned problem, a shield in which a liquid crystal display device is housed has been equipped with a fun or a heat sink.
Hereinbelow is explained conventional light source units used in a liquid crystal display device.
FIG. 1A is a perspective view of a conventional liquid crystal display device, and FIG. 1B is a cross-sectional view taken along the line 1Bxe2x80x941B in FIG. 1A.
The illustrated liquid crystal display device 1 is comprised of a liquid crystal panel 2, a shield 3 in which the liquid crystal panel 2 and a light source unit 4 (see FIG. 1B) are accommodated, a heat radiator 7 formed on a rear surface of the shield 3, and parts 8 mounted on a rear surface of the shield 3.
A shield front 31a defining a front surface of the shield 31 is formed with an opening 31a through which a part of the liquid crystal panel 2 is exposed. A exposed portion of the liquid crystal panel 2 defines a display screen of the liquid crystal display device 1.
As illustrated in FIG. 1B, the heat radiator 7 is mounted on a shield rear 33 defining a rear surface of the shield 3. The shield rear 33 is composed of metal having high thermal conductivity and being light, such as aluminum.
Heat generated in the light source unit 4 is radiated through the shield rear 33 having high heat radiation property.
As illustrated in FIG. 1B, the liquid crystal display device 1 includes the liquid crystal panel 2 in the form of a plate, a light-diffusion plate 5, and the light source unit 4. They are arranged in parallel with one another in facing relation to one another.
The liquid crystal panel 2 is supported by being sandwiched between the shield front 31 and a shield center 32. The light-diffusion plate 5 and the light source unit 4 are supported by being sandwiched between the shield center 32 and the shield rear 33.
The heat radiator 7 and the parts 8 are mounted on a rear surface of the shield rear 33.
The shield front 31, the shield center 32 and the shield rear 33 are coupled to one another through screws.
Hereinbelow is explained a structure of the light source unit 4. A structure of the light source unit 4 is grouped into a beneath-arrangement type and a side light type.
FIG. 2A is a cross-sectional view of a liquid crystal display device including a beneath-arrangement type light source unit, and FIG. 2B is a cross-sectional view of a liquid crystal display device including a side light type light source unit.
As illustrated in FIG. 2A, a beneath-arrangement type light source unit 4 is comprised of a reflector 43 positioned in a dish-shaped portion 4a (lamp house) of the shield rear 33, a plurality of pillar-shaped light sources 41 near and along the reflector 43, and a light-diffusion plate (not illustrated) covering the lamp house 4a and spaced away from the light sources 41.
The light-diffusion plate prevents non-uniformity in brightness.
As illustrated in FIG. 2B, a side light type light source unit 4 is comprised of a light-guide plate 42 in the form of a plate, a pillar-shaped light source 41 located adjacent to a side of the light-guide plate 42, and a reflector 43 surrounding the light source 41.
The light-guide plate 42 is composed of highly light-permeable acrylic plate. A light emitted from the light source 41 passes through the light-guide plate 42, and illuminates a rear surface of the liquid crystal panel 2 through an opening 32a formed with the shield center 32.
Dots are printed over a rear surface of the light-guide plate 42 facing the shield rear 33 in order to prevent non-uniformity in brightness.
Japanese Unexamined Patent Publication No. 10-172512 has suggested a light source unit which prevents an increase in temperature in an object to which a light is to be radiated.
As illustrated in FIG. 3, the suggested light source unit 4 includes a light source 41 comprised of an elongate glass bulb containing an electrically discharging medium, and an outer glass pipe 49 spaced away from the light source 41 to thereby define a vacuum layer 41b therebetween. A light emitted from the light source 41 passes through an entire surface 41a of the glass bulb 41, and heat radiated from the light source 41 through the entire surface 41a is absorbed in the vacuum layer 41b. Thus, it would be possible to reduce heat radiation to an object which is to be illuminated by the light source 41.
As mentioned earlier, if a brightness at a display surface of a liquid crystal display device is to be increased, heat radiation to a liquid crystal panel from a light source unit would be increased in dependence on an increase in the brightness.
Hence, the heat radiation has to be suppressed in order not to deteriorate a brightness and a display quality of a liquid crystal panel.
However, the conventional liquid crystal display device including a heat radiator mounted on a rear surface of a shield could be improved only in that the shield and/or heat radiator are(is) composed of material having high thermal conductivity, or that the heat radiator is designed to have a surface area as wide as possible.
In accordance with the light source unit suggested in the above-mentioned Japanese Unexamined Patent Publication No. 10-172512, interruption of heat to an object (liquid crystal panel) from the light source unit could be obtained to some degree. However, only such adiabatic effect could accomplish just a limited increase in output power of the light source unit.
Specifically, if an output power of the light source unit is increased, a temperature in the glass bulb 41 would be raised more than necessary due to heat interruption from an atmosphere, resulting in reduction in a light-emitting efficiency and reduction in a lifetime caused by degradation of phosphor and/or electrodes.
If the above-mentioned light source unit is applied to a side light type light source unit, multiple reflection would occur to the reflector 43, resulting in light loss.
In addition, since the outer glass pipe 49 does not have a light diffusion function, a light diffusion plate has to be newly added to the light source unit, causing a problem that the light source unit unavoidably becomes larger in size.
In view of the above-mentioned problems in the conventional light source units, it is an object of the present invention to provide a light source unit which is capable of preventing heat accumulation in an object to which a light is radiated.
In one aspect of the present invention, there is provided a light source unit including (a) a light source having a main surface through which a light emitted from the light source passes towards an object, (b) a light-permeable substrate located between the main surface of the light source and the object, (c) a first seal sandwiched between the main surface of the light source and a surface of the light-permeable substrate and defining a first closed space together with the main surface and the surface of the light-permeable substrate, the first closed space being in vacuum, and (d) a heat radiator equipped with the light source for outwardly radiating heat generated in the light source.
For instance, the light source may includes (a) a first substrate, (b) a second substrate, (c) a second seal sandwiched between the first and second substrates and defining a second closed space together with the first and second substrates, noble gas being sealed in the second closed space.
As an alternative, the light source may includes (a) a first substrate facing the light-permeable substrate, (b) a second substrate, (c) a third substrate, (d) a second seal sandwiched between the first and second substrates and defining a second closed space together with the first and second substrates, noble gas being sealed in the second closed space, (e) a third seal sandwiched between the second and third substrates and defining a third closed space together with the second and third substrates, the third seal being formed with a first through-hole through which heat accumulated in the third closed space passes outwardly of the third closed space.
The light source unit may further include a shield covering the light source therewith, the shield being formed with a second through-hole which is in communication with the first through-hole.
The light source unit may further include a dish-shaped shield in which the light source is set and which defines a closed space together with the light-permeable substrate.
The light source unit may further include a shield, and a light-guide plate located in the shield, and having a first surface through which a light emitted from the light source passes, and a second surface of which the light source is positioned in the vicinity.
It is preferable that the dish-shaped shield is formed with at least one through-hole through which heat generated in the light source is radiated.
It is preferable that the shield is formed with at least one through-hole through which heat generated in the light source is radiated.
It is preferable that the first closed space is kept in a pressure equal to or smaller than 1.33xc3x97103 Pa.
It is preferable that the light-permeable substrate has a function of diffusing a light emitted from the light source.
In another aspect of the present invention, there is provided a method of fabricating a light source unit, including the steps of (a) forming at least one electrode on a first surface of a first substrate, (b) forming a first dielectric layer on the first surface such that the electrode is covered with the first dielectric layer, (c) forming a second dielectric layer on a first surface of a second substrate, (d) forming a phosphor layer on the second dielectric layer, (e) facing the first substrate, the second substrate and a third substrate one another with a spacer being sandwiched between any two substrates among the first to third substrates such that the phosphor layer of the second substrate faces the dielectric layer of the first substrate and that the third substrate is adjacent to the second substrate, (f) making a first closed space vacuous which first closed space is defined by the first substrate, the second substrate and the spacer, (g) introducing noble gas into the first closed space, and (h) making a second closed space vacuous which second closed space is defined by the second substrate, the third substrate and the spacer.
It is preferable that the second closed space is kept in pressure equal to or smaller than 1.33xc3x97103 Pa in said step (h).
The method may further include the step of forming a protection layer on the first dielectric layer.
The method may further include the step of coating a glass having a low fusing point, around the first and second substrates.
The method may further include the step of applying a light diffusion function to at least one of upper and lower surfaces of the third substrate.
The method may further include the steps of forming at least one through-hole with the first substrate from which air is exhausted from the first closed space, and sealing the through-hole after air has been exhausted from the first closed space.
The method may further include the steps of forming at least one through-hole with the third substrate from which air is exhausted from the second closed space, and sealing the through-hole after air has been exhausted from the second closed space.
The method may further include the steps of forming at least one through-hole with the spacer from which air is exhausted from the first closed space, the spacer connecting the first and second substrates to each other, and sealing the through-hole after air has been exhausted from the first closed space.
The method may further include the steps of forming at least one through-hole with the spacer from which air is exhausted from the second closed space, the spacer connecting the second and third substrates to each other, and sealing the through-hole after air has been exhausted from the second closed space.
It is preferable that the first closed space is made vacuous in the step (f) by exhausting air therefrom.
It is preferable that the first closed space is made vacuous in the step (f) by carrying out the step (e) in a vacuum chamber.
It is preferable that the second closed space is made vacuous in the step (h) by exhausting air therefrom.
It is preferable that the second closed space is made vacuous in the step (h) by carrying out the step (e) in a vacuum chamber.
In still another aspect of the present invention, there is provided a liquid crystal display unit including (a) one of the above-mentioned light source unit, and (b) a liquid crystal display device receiving a light from the light source unit to display a designated image.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
In accordance with the above-mentioned invention, it is possible to reduce heat radiation to an optical part such as a liquid crystal panel or a light diffusion plate from a light source unit, and to enhance an output power of a light source unit by virtue of efficient heat radiation.
This ensures that an object can be lighted with a higher brightness.
By applying the present invention to a beneath-arrangement type light source unit, a sufficient distance can be ensured between a light source and an optical part such as a light diffusion plate, ensuring reduction in non-uniformity in a brightness.
In addition, the present invention can reduce fabrication costs and the number of fabrication steps.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.